A diesel particulate trapping filter including an oxidative catalyst and a filter has traditionally been known. Patent Document 1 also discloses an example of an exhaust gas purifying apparatus that includes the diesel particulate trapping filter.
The exhaust gas purifying apparatus is configured to activate the oxidative catalyst by increasing the temperature of the exhaust gas. When the oxidative catalyst is activated, the oxides of nitrogen in the exhaust gas are oxidized to produce nitrogen dioxide. Because nitrogen dioxide has a strong oxidizing action, the PM (particulate matter) on the filter is oxidized and removed. To increase the temperature of the exhaust gas, exhaust gas reduction, intake air reduction, delaying of the main injection timing, and the like are conducted. In addition to the above control, the exhaust gas purifying apparatus is configured to further increase the temperature of the exhaust gas entering the filter (a filter entrance temperature) by supplying the fuel to the activated oxidative catalyst using post-injection. When the filter entrance temperature exceeds the combustion temperature of the PM (400° C.), the PM on the filter is oxidized and removed by oxygen in the exhaust gas. Compared to the oxidization by nitrogen dioxide, the combustion with oxygen can quickly remove the PM. The temperature of the exhaust gas is therefore increased using the post-injection when the filter is caused to completely recover.